1. Field of the Invention
The present invention relates to a lens barrel, and particularly, to a lens barrel in which a limitation is set on a rotation of a cam barrel.
2. Related Background Art
In a lens barrel mounted on the body of a camera, a focusing operation for moving lens groups in the direction of the optical axis is performed in order to bring a distant object into focus. Such focusing operation is conducted by a photographer or an operator by rotating a manual focusing ring which is provided in the lens barrel. When the manual focusing ring is rotated, the cam barrel in the lens barrel is rotated, whereby the lens group is moved in the direction of the optical axis through the cam mechanism.
Recently, such a lens barrel has been developed and already put on the market, which enables automatic focusing for moving the lens group with a motive power from a motor incorporated, for example, in the camera body while enabling the manual focusing mentioned above. Such lens barrel which is capable of automatic focusing is provided with a coupler member for receiving a motive power from the motor in the camera body, and the motive power supplied through the coupler member is used to rotate the cam barrel, thereby moving the lens group in the direction of the optical axis.
FIG. 3 is a cross-sectional view of the lens barrel of such conventional technique in the direction of the optical axis. Referring to FIG. 3, a cam barrel 2 which has a cam groove 2a is fitted in the outer periphery of a fixed barrel 1 to be freely rotatable. An outer fixed barrel 3 is fixed to the fixed barrel 1 with a screw 13. A manual focusing ring 4 is attached to the tip end of the outer fixed barrel 3 to be freely rotatable.
One end of an interlocking member 5 which serves as a manual power transmission mechanism is attached to the manual focusing ring 4 with a screw 45. Two interlocking members 5 which are provided in upper and lower parts symmetrically with the optical axis therebetween are two plate-like members which are extended toward the camera side. The tip end 5a of each interlocking member 5 is engaged between two projected portions 2b (only one is shown) which are formed in parallel in the circumferential direction on the outer peripheral of the cam barrel 2. That is, the interlocking members 5 function to couple the manual focusing ring 4 and the cam barrel 2 for rotating together.
A coupler member 8 is provided adjacent to the lower interlocking member 5 and is supported to be freely rotatable with respect to the fixed barrel 1. The coupler member 8 as a motor power transmission mechanism is provided with a gear portion 8a at the left end thereof and a connecting portion 8b at the right end. The connecting portion 8b can be freely engaged with a driving portion (not shown) projected from the camera body. The gear portion 8a of the coupler member 8 is meshed with a gear portion 2c which is formed on the outer periphery of the cam barrel 2.
A lens moving frame 6 serving as a supporting frame supports lens groups L1, L2 and is fitted in the fixed barrel to be movable along the optical axis. A pair of pins 7 are attached to the outer periphery of the lens moving frame 6 and fitted in a straight advancement groove la formed in the fixed barrel 1 and a cam groove 2a formed spirally on the cam member 2, respectively.
An operation of the lens barrel according to the prior art will be described below. First, when the photographer rotates the manual focusing ring 4, the cam barrel 2 is rotated as stated, and the lens moving frame 6 moves straight along the optical axis, whereby a manual focusing operation is conducted.
On the other hand, when an automatic focusing operation is conducted, the coupler member 8 which is mounted on the fixed barrel 1 to be freely rotatable rotates, upon receiving a motor drive from the camera body (not shown), the cam barrel 2 around the optical axis through the gear portion 8a provided in the coupler member 8 and the gear portion 2c engaged therewith, thereby moving the lens moving frame 6 in the direction of the optical axis.
Incidentally, since the manual power of the photographer is comparatively strong, when the manual focusing ring 4 is rotated carelessly toward the end of movement of the lens moving frame 6 (e.g. to the infinity position of the photographing lens), a large load is applied to the interlocking member 5 or the cam mechanism so that deformation or destruction of such member or mechanism may be brought about. For this reason, the manual focusing ring 4 usually has a rotation limit for preventing a rotation by not less than a predetermined angle.
More specifically, a projection 3a is formed to project inward in a direction perpendicular to the optical axis. It is arranged that a vicinity of an installing portion of the interlocking member 5 (that is, a portion of the interlocking member 5 at which an end thereof is attached to the manual focusing ring 4 with the screw 45) is brought into contact with such projection 3a, so as to limit a rotation of the manual focusing ring 4. Since the vicinity of the installing portion of the interlocking member 5 has a comparatively high rigidity, if the projection 3a is brought into contact therewith under great pressure, the interlocking member 5 is hardly deformed.
On the other hand, it is arranged that, when the automatic focusing operation is performed, the interlocking member 5 is rotated integrally with the cam barrel 2 upon receiving a motive power therefrom, so that when the interlocking member 5 is brought into contact with the projection 3a, further rotation of the cam barrel 2 is limited.
The interlocking member 5 is a plate-like member having the width of 5 mm to 10 mm and is fixed to the manual focusing ring 4 in a cantilever manner and, therefore, comparatively flexible. As a result, even if the manual focusing ring 4 is stopped, the tip end 5a thereof is movable to some extent based on such flexibility. Also, in a power transmission path from the interlocking member 5 to the coupler member 8, there are present a variety of power transmitting elements which are engaged with each other, so that a large backlash may be generated when backlashes between the elements are accumulated, even if each backlash is small.
Accordingly, if the interlocking member 5 is brought into contact with the projection 3a of the fixed barrel 3 when the automatic focusing is operated, the coupler member 8 is not stopped immediately, but is rotated to some extent based on the above-mentioned deformation or backlash of the components, which is called the excessive rotation. However, since the lens moving frame 6 has already reached the moving end, if the coupler member 8 is rotated further, an angle of rotation of the coupler member 8 and an amount of the movement of the lens moving frame 6 are not corresponding to each other, so that the subsequent automatic focusing control may be erroneous. In addition, if the coupler member 8 is excessively rotated, the components of the lens barrel may be interfered with each other.
On the other hand, it is possible to suppress the excessive rotation of the coupler member 8 by enhancing the deflection rigidity of the interlocking member 5, for example. However, in order to enhance the deflection rigidity of the interlocking member 5, it is required to enlarge the cross-sectional form of the interlocking member 5, which brings about enlargement of the lens barrel.